Screw fastening machine

Abstract

To provide a screw fastening machine which enables easy change of pressing force applied to a fastening tool.SOLUTION: A screw fastening machine includes: a motor 32; a fastening tool 35 which is rotationally driven by driving the motor 32 and in which a screw may be engaged with a tip; and an air cushion mechanism which is fitted in a rear end of the fastening tool 35 and holds the fastening tool 35 in a shock-absorbing manner. The air cushion mechanism has a shaft joint 33 which connects the motor 32 with the fastening tool 35 and biases the fastening tool 35 by compressed air supplied to the inside thereof. The shaft joint 33 has an exhaust hole 334 formed for exhausting compressed air therein. The exhaust hole 334 is characterized in that an opening at the external side is formed wider than an opening at the insertion hole side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a screw driving machine for fastening screws into a workpiece. [Background technology]

[0002] Conventionally, as shown in Patent Document 1, there is known a screw driving machine in which an elevation drive source raises and lowers a screw driving unit equipped with a driver bit and a motor. Such a screw driving machine is equipped with a compression spring that constantly urges the driver bit in a direction away from the motor, and when this compression spring flexes, the driver bit moves axially relative to the motor. Therefore, when a screw fitted to the driver bit comes into contact with a workpiece, the compression spring flexes, thereby absorbing the impact of the contact, which has the advantage of preventing damage to the workpiece and the screw. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-315071 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional screwdrivers were designed so that the compression spring biased the driver bit toward the workpiece, so when changing the pressing force of the driver bit, it was necessary to disassemble the screwdriver and replace the compression spring.

[0005] Therefore, an object of the present invention is to provide a screwdriver that can easily change the pressing force of a driver bit. [Means for solving the problem]

[0006] The present invention has been made in view of the above-mentioned problems, and provides a screw driving machine comprising: a motor; a tightening tool that is driven to rotate by the motor and has a tip that can engage a screw; and an air cushion mechanism that fits onto the rear end of the tightening tool and cushions the tightening tool, the air cushion mechanism having a shaft coupling that connects the drive shaft of the motor to the tightening tool, the shaft coupling having an insertion hole into which the rear end of the tightening tool is inserted and an exhaust hole that communicates with the insertion hole, the insertion hole being configured so that pressurized air is supplied into a space formed by the inner wall of the insertion hole and the rear end of the tightening tool, and the pressurized air inside is exhausted to the outside through the exhaust hole, the exhaust hole being configured so that it gradually widens from an opening on the insertion hole side to an opening on the outside side. Preferably, the exhaust hole is formed in a stepped shape with a narrow portion opening toward the insertion hole and a wide portion opening toward the outside. Preferably, the narrow portion is configured to gradually widen toward the outside. Furthermore, it is preferable that the wide portion be wider than the maximum portion of the narrow portion. Moreover, it is preferable that the exhaust hole is configured in the shape of an elongated hole. [Effects of the Invention]

[0007] The screw driver of the present invention has the advantage that the pressing force of the tightening tool can be easily changed by changing the pressure of the pressurized air supplied to the shaft coupling. In addition, because the exhaust hole is configured to gradually widen from the insertion hole side to the outside, the amount of air that flows out can be reduced and dust and the like are less likely to clog the exhaust hole. Furthermore, by configuring the exhaust hole in a stepped shape with a narrow portion and a wide portion, there are also advantages such as making it easier to process the narrow portion that opens onto the insertion hole side, and facilitating high-precision manufacturing. Furthermore, since the narrow portion is configured to gradually widen toward the outer periphery, there is also the advantage that dust and the like are less likely to get stuck in the narrow portion. Furthermore, since the exhaust hole is configured as an elongated hole, the amount of air exhausted from the exhaust hole changes intermittently, which has the advantage that the positional relationship between the tightening tool and the shaft coupling can be constantly grasped. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a partially cross-sectional side view showing the structure of a screw driver according to the present invention. [Figure 2] 1 is an enlarged, partially cutaway, cross-sectional side view showing the structure of a main part of a screw fastener according to the present invention. [Figure 3] FIG. 3 is an enlarged view of part A in FIG. 2. [Figure 4] 2 showing a state transitioning from FIG. 3 to the next state. FIG. [Figure 5] 4(a) is a cross-sectional view taken along line BB in FIG. 3, and (b) is an enlarged view of the main part of (a). DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will be described below with reference to the drawings. In Figures 1 and 2, reference numeral 10 denotes a screw driver that fastens a screw (not shown) into a workpiece (not shown). This screw driver 10 has a position control unit 20, a screw tightening unit 30 supported by this position control unit 20, and a control unit that controls the driving of the position control unit 20 and the screw tightening unit 30. The screw has a head and a leg, and a male thread is formed on the outer periphery of the leg.

[0010] The position control unit 20 includes a base member 21 extending vertically, with an upper plate 22 and a lower plate 23 extending horizontally fixed integrally to the upper and lower ends of the base member 21. A guide rod 24 extending parallel to the base member 21 is provided between the upper plate 22 and the lower plate 23. A tool table 25 configured to slide freely is attached to the guide rod 24 so as to be able to move up and down. An AC servo motor 26 for lifting (hereinafter referred to as the lift motor 26) is mounted on the upper plate 22, and a ball screw 27 is integrally and rotatably connected to the drive shaft of the lift motor 26. The ball screw 27 is provided between the upper plate 22 and the lower plate 23, and the tool table 25 is connected to the ball screw 27 via a drive nut (not shown) that moves up and down as the ball screw 27 rotates. With this structure, the tool table 25 can be raised and lowered along the guide rod 24 by receiving rotational drive from the lift motor 26.

[0011] As shown in FIG. 2, the screw tightening unit 30 has a hollow cylindrical motor holder 31 disposed above the tool table 25 of the position control unit 20. A fastening AC servo motor 32 (hereinafter referred to as the fastening motor 32) is fixed to the motor holder 31 with its drive shaft inserted into the motor holder 31, and a shaft coupling 33 is connected to the drive shaft of the fastening motor 32 so that the shaft coupling 33 can rotate integrally with the motor. An insertion hole 331 with a circular cross section is formed in the underside of the shaft coupling 33, and a fitting hole 332 with a substantially rectangular cross section is formed continuously at the bottom of the insertion hole 331. An elongated sliding hole 333 extending in the axial direction intersects with the insertion hole 331. A connecting pin 34 configured to be able to move up and down is inserted through the sliding hole 333, and a driver bit 35 is suspended from the connecting pin 34. The driver bit 35 is a generally cylindrical member having approximately the same size as the insertion hole 331, and has at its upper end a fitting portion 351 that fits into the fitting hole 332, while at its lower end a drive portion that fits into the head of the screw. With this structure, the driver bit 35 can rotate integrally with the shaft coupling 33 and the drive shaft of the fastening motor 32, and can move relative to the shaft coupling 33 and the fastening motor 32 by the distance that the connecting pin 34 can move along the slide hole 333.

[0012] The air cushion mechanism, which is a main part of the present invention, will now be described. As shown in FIG. 2, the motor holding portion 31 has a through-hole formed therein into which a hose coupling 311 can be inserted, and an air supply hose (not shown) extending to a compressor, which is an example of air supply means, is connected to the hose coupling 311. A plurality of vent holes are formed near the bottom of the side wall of the fitting hole 332, extending perpendicular to the fitting hole 332 and opening toward the outer periphery of the shaft coupling 33. A cylindrical seal member 36 is provided between the motor holding portion 31 and the shaft coupling 33 to airtightly connect the hose coupling 311 and the fitting hole 332. A connection hole 361 is formed in the seal member 36 to connect the hose coupling 311 and the fitting hole 332, and the gap between the seal member 36 and the motor holding portion 31 and the shaft coupling 33 is airtightly maintained by airtight packings 362, 363, 364, and 365 attached above and below the connection hole 361. In this embodiment, the airtight gaskets 362, 363 that maintain an airtight seal between the seal part 36 and the motor holding part 31 are gaskets with a circular cross section, while the airtight gaskets 364, 365 that maintain an airtight seal between the seal part 36 and the shaft coupling 33 are gaskets with a Y-shaped cross section that allow rotation of the shaft coupling 33. Bearings 366, 367 that rotatably hold the shaft coupling 33 are disposed above and below the seal part 36, and these bearings 366, 367 hold the motor holding part 31 and the shaft coupling 33 together with snap rings. With the above-described structure, pressurized air supplied from the compressor is supplied to the shaft coupling 33 through the hose coupling 311 and the connection hole 361 of the seal part 36 and enters through the air vent of the shaft coupling 33, pressurizing the inside of the fitting hole 332. As a result, the air cushion mechanism can urge the driver bit 35 toward the tip end and hold it in a cushioning manner.

[0013] Furthermore, a connecting hole 352 extending in the axial direction is formed in the upper end surface of the fitting portion 351 of the driver bit 35, and a plurality of through holes extending perpendicular to the connecting hole 352 and penetrating to the outer surface of the fitting portion 351 are formed in the bottom of this connecting hole 352. Therefore, pressurized air supplied into the shaft coupling 33 passes through the fitting hole 332 and the connecting hole 352 and enters the insertion hole 331 of the shaft coupling 33. Furthermore, an exhaust hole 334 penetrating to the outer periphery of the shaft coupling 33 is formed in the shaft coupling 33 near the bottom of the insertion hole 331, and the exhaust hole 334 is configured as an elongated hole extending in the axial direction of the shaft coupling 34. Therefore, air that has entered the insertion hole 331 can be exhausted to the outside. Moreover, the driver bit 35 has an annular groove on its outer periphery, and this annular groove houses an airtight packing 353 that maintains an airtight seal between the driver bit 35 and the shaft coupling 33. With this structure, the pressurized air that is supplied from the compressor and urges the driver bit 35 downward reaches the insertion hole 331 through the connecting hole 352 of the driver bit 35, and is then exhausted to the outside through the exhaust hole 334. Note that the exhaust hole 334 is designed so that, as shown in Figures 3 and 4, the driver bit 35 rises relative to the shaft coupling 33 and the fastening motor 32 and is gradually blocked from below by the airtight packing 353. Therefore, the size of the exhaust hole 334 changes depending on the position of the driver bit 35 with respect to the shaft coupling 33, and the amount of pressurized air exhausted from the exhaust hole 334 increases or decreases.

[0014] Furthermore, as shown in Figures 5(a) and 5(b), the exhaust hole 334 has a stepped shape with a narrow portion 335 opening radially inward and a wide portion 336 opening radially outward. The narrow portion 335 has a tapered shape that gradually widens radially outward. The wide portion 336 is configured so that its width is sufficiently wider than the maximum width of the narrow portion 335 and its radial dimension is sufficiently longer than that of the narrow portion 335. Because the narrow portion 335 is located radially inward, the amount of air flowing out from the shaft coupling 33 to the outside is reduced. This reduces the compressor's drive force and improves energy efficiency. Furthermore, the tapered shape of the narrow portion 335 prevents dust, metal powder due to wear, and other debris from accumulating inside the narrow portion 335. Furthermore, since the wide portion 336 is formed on the outer side of the narrow portion 335, the radial dimension of the narrow portion 335 is shortened, and therefore the narrow portion 335 can be manufactured easily and inexpensively.

[0015] The compressor is equipped with a measuring means for measuring the flow rate of the supplied air. This measuring means is connected to the control unit and constantly notifies the control unit of the flow rate. This allows the control unit to constantly monitor the amount of air supplied by the compressor, i.e., the amount of air exhausted from the exhaust holes 334. As a result, when air is supplied at a constant pressure, the increase or decrease in the exhaust rate can be used to determine the blocking status of the exhaust holes 334 by the driver bit 35, i.e., the relative positional relationship between the driver bit 35 and the coupling 33. Furthermore, the exhaust holes 334 are positioned such that, when the connecting pin 34 is in contact with the lowest part of the sliding hole 333 as shown in FIG. 3 , the lowest exhaust hole 334 is located near the boundary between the substantially cylindrical main part of the driver bit 35 and the fitting portion 351. Therefore, the lowest exhaust hole 334 is immediately blocked when the driver bit 35 begins to move relative to the coupling 33.

[0016] Meanwhile, a hollow cylindrical guide member 37 is fixed below the tool base 25 of the position control unit 20 so as to cover the driver bit 35, and a screw guide 371 is suspended from this guide member 37 so as to be relatively movable in the axial direction. This screw guide 371 contains the driver bit 35 so as to be rotatable and relatively movable in the axial direction, and is constantly urged downward by a cushion spring 372 contained between the screw guide 371 and the tool base 25. A vacuum pump (not shown), which is an example of suction means, is connected to the screw guide 371, and an accommodation section capable of containing the screw is formed at its lower end opening.

[0017] Also, a chuck unit 40 capable of temporarily holding a screw pressure-fed from an external component supply device is fixed to the lower plate 23 in an extension line of the screw guide 371 and the driver bit 35. Similar to the chuck unit 40 disclosed in Japanese Patent Laid-Open Publication No. 9-174349, this chuck unit 40 includes a component supply hose 41 continuing to the component supply device, and a pair of chuck jaws 42 capable of holding a screw that has passed through this component supply hose 41 in an extension line of the screw guide 371 and the driver bit 35. When pressed from above by the screw guide 371 or the driver bit 35, the chuck jaws 42 swing and are configured to be able to retract from an extension line of the screw guide 371 and the screw tightening unit 30.

[0018] The control unit is connected to the lifting motor 26 of the position control unit 20, the fastening motor 32 of the screw tightening unit 30, a compressor, a vacuum pump, and a parts supply device, and is configured to be able to control the drive of these.

[0019] Next, the operation of the screw driving tool 10 configured as above will be described. When a drive signal is input, the control unit drives the component supply device to pressure-feed the screw toward the chuck unit 40, where it is held by the chuck jaws 42 through the supply hose. After the screw is held in the chuck unit 40, the control unit drives the compressor, the vacuum pump, and the lift motor 26. This urges the driver bit 35 downward, and the screw tool, which is sucking air from the lower opening of the screw guide 371, descends toward the chuck unit 40. During this movement, the screw guide 371 picks up the screw held in the chuck unit 40 and stores it in the lower opening. Then, the tip of the screw guide 371 pushes open the chuck jaws 42, and the screw tightening unit 30 descends. During this descent, the control unit drives the fastening motor 32 to rotate the driver bit 35.

[0020] As described above, the screw tightening unit 30, which has adsorbed and held the screw, further descends until the lower end of the screw guide 371 comes into contact with the workpiece, at which point only the screw guide 371 stops descending. As a result, the driver bit 35 descends inside the screw guide 371 while deflecting the cushion spring 372. As a result, the driver bit 35 comes into contact with the screw held in the screw guide 371 and presses the screw toward the workpiece. At this time, because the driver bit 35 is rotating, the drive part of the driver bit 35 engages with the head of the screw. After that, the screw comes into contact with the workpiece and rotates integrally with the driver bit 35, thereby being tightened into the workpiece.

[0021] As described above, when the screw contacts the workpiece and the descent of the screw and driver bit 35 stops, the driver bit 35 rises relative to the shaft coupling 33, which continues to descend. As a result, the driver bit 35 closes the lowest exhaust hole 334, as shown in FIG. 4. When the exhaust hole 334 is closed in this manner, the amount of exhaust air flowing out through the exhaust hole 334 decreases, and the amount of air supplied from the compressor to the motor holder 31 also decreases accordingly. Therefore, the compressor's measuring means notifies the control unit of the decrease in the air supply. Upon receiving this notification, the control unit determines that the screw has come into contact with the workpiece and slows down the descent speed of the position control unit 20. Being able to detect that the screw has come into contact with the workpiece in this way allows for screw tightening to be performed without being affected by warpage of the workpiece.

[0022] When fastening a screw into a workpiece as described above, the fastening motor 32 outputs a pre-tightening torque until the screw seats on the workpiece, and then outputs a final fastening torque that is greater than the pre-tightening torque after the screw seats on the workpiece. When the final fastening torque is output, the control unit stops driving the fastening motor 32 and drives the lifting motor 26 to raise the screw fastening unit 30. At this time, as the screw fastening unit 30 rises, the driver bit 35 is forced by the pressurized air and again descends relative to the shaft coupling 33. This returns the driver bit 35 and the shaft coupling 33 to the initial positional relationship shown in FIG. 3.

[0023] The screw driver 10 configured as described above can freely change the thrust applied to the driver bit 35 by changing the pressure of the compressed air supplied from the compressor. This allows the appropriate thrust for screw tightening to be applied without disassembling the screw driver 10. Furthermore, as described above, the moment when the screw contacts the workpiece can be determined from the decrease in the air supply. Therefore, when tightening a normal screw, the position where the screw contacts the workpiece and the air supply decreases (hereinafter referred to as the decrease position) can be pre-programmed into the position control unit 20. By comparing the actual position where the air supply decreases during screw tightening with the preset air decrease position, it is possible to check whether the screw is normal and has the desired length. Furthermore, because the driver bit 35 is biased by compressed air, it can be constantly biased with a constant force regardless of its relative position with the shaft coupling 33. This allows the driver bit 35 to function as a brake from the moment it contacts the workpiece. Therefore, even if the descending speed of the screw tightening unit 30 is faster than normal, the screw tightening unit 30 can be slowly decelerated, and the upper end of the sliding hole 333 of the shaft coupling 33 can be prevented from colliding with the connecting pin 34. As a result, damage to the workpiece loaded with the weight of the screw tightening unit 30 via the driver bit 35 and the screw can be prevented.

[0024] Furthermore, the screw driver 10 has an advantage that the narrow portion 335 of the exhaust hole 334 is tapered, so that dust and metal powder due to wear are less likely to become clogged inside the narrow portion 335 even after long-term use. Furthermore, the exhaust hole 334 has a stepped shape consisting of the narrow portion 335 and the wide portion 336, so that the amount of air that flows out from the shaft coupling 33 to the outside can be reduced, which improves energy efficiency and is environmentally friendly.

[0025] The screw driving tool 10 according to the present invention is not limited to the above-described configuration, and various modifications are possible without departing from the spirit and scope of the invention. For example, the exhaust hole is not limited to a stepped shape, and may be configured as a tapered shape that gradually widens from the inner periphery to the outer periphery of the shaft coupling. Furthermore, while the screw driving tool 10 has only one exhaust hole 334 in the circumferential direction, this is not limited to this, and two or more exhaust holes may be formed. Furthermore, as long as the relative position of the tightening tool can be detected, the exhaust hole 334 is not limited to an elongated hole extending in the vertical direction, and may be an elongated hole extending in the spiral direction, or a structure in which multiple through holes are provided with a predetermined gap in the vertical direction. [Explanation of symbols]

[0026] 10...Screw tightening machine 20... Position control unit 30...Screw tightening unit 31 ... Motor holding part 311... Hose fitting 32 ... Fastening motor 33... Shaft coupling 331... Insertion hole 332... Fitting hole 333…Sliding hole 334... Exhaust vent 335…Narrow part 336… Wide section 34 ... Connecting pin 35... Driver bit 351... Fitting part 352... Connection hole 36 ... Sealing parts 361... Connection hole 40...Chuck unit

Claims

1. A motor; a fastening tool that is driven to rotate by the motor and has a tip that can engage a screw; an air cushion mechanism that fits onto the rear end of the tightening tool and cushions the tightening tool; the air cushion mechanism has a shaft coupling that connects a drive shaft of a motor and a tightening tool; The shaft coupling is formed with an insertion hole into which a rear end of a tightening tool is inserted and an exhaust hole communicating with the insertion hole, In a screw driving tool, the insertion hole is configured so that the tightening tool is biased by pressurized air supplied into a space formed by the inner wall of the insertion hole and the rear end of the tightening tool, and the internal pressurized air is exhausted to the outside through the exhaust hole, The screw driving tool is characterized in that the exhaust hole is configured to gradually widen from the opening on the insertion hole side to the opening on the exterior side.

2. The screw driver according to claim 1, wherein the exhaust hole has a stepped shape in which a narrow portion opening toward the insertion hole and a wide portion opening toward the outside are connected.

3. 3. The screw driver according to claim 2, wherein the narrow portion is configured to gradually widen toward the outside.

4. 4. The screw driver according to claim 3, wherein the wide portion is wider than the maximum portion of the narrow portion.

5. The screw driver according to claim 1, wherein the exhaust hole is configured in the shape of an elongated hole.

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